Epichloë species are fungal symbionts (endophytes)
of grasses, many of which are benign or mutualistic and have a balance of horizontal
(contagious) and vertical (seed-borne) transmission, whereas others mainly transmit
horizontally and are more antagonistic. Over the past eight years several Epichloë
species have been described based largely on the biological species concept.
We conducted a multi-gene phylogenetic analysis to evaluate these endophytes
as phylogenetic species, and thereby assess the relationship of phylogenetic
and biological species. Variation mainly in introns of genes encoding b-tubulin
(tub2), translation elongation factor 1-a (tef1) and actin (act1) provided robust
phylogenetic signal distinguishing the described Epichloë
species. Outgroup rooting split the genus into two major groups. One group included
most species with balanced transmission strategy, and in this group the phylogenetic
and biological species concepts corresponded well. In contrast, these species
concepts poorly corresponded for the other group, the Epichloëtyphina
complex, with predominantly antagonistic, horizontally transmitted endophytes.
We hypothesize that the balance of vertical and horizontal transmission promotes
ecological (host) specialization and subsequent genetic isolation as mechanisms
promoting speciation; whereas strict horizontal transmission may select for
broader host ranges, slow the development of genetically isolated species, and
thereby increase lineage sorting effects that cause conflicts between phylogenetic
and biological species.